The invention relates to a braking device primarily for a linear, screw actuator, the device being of the kind known as a xe2x80x9cno-backxe2x80x9d device.
The principle of operation of so-called xe2x80x9cno-backxe2x80x9d braking devices is known in the art in connection with actuators for positioning a flight control surface on an aircraft. The operation of one type of no-back device is described, for example, in U.S. Pat. No. 3,583,248, the disclosure of which is incorporated herein by reference. The role of such a no-back device is to facilitate elimination of the effect of any forces tending to aid or oppose input torque applied to a screw of an actuator, with a view to substantially preventing such forces back-driving the screw shaft and thus the prime mover driving the shaft. It is recognised that there will be operative conditions in which the no-back device of an actuator is operative while drive is being transmitted to the shaft from the associated prime mover and in such situations the no-back device can be subjected to loadings giving rise to high wear rates. It is an object of the present invention to provide a no-back device which is more tolerant of such high wear rate operating conditions.
In accordance with the invention, there is provided a no-back device for an actuator having a screw shaft extending along an axis and a brake element fixed for rotation with the shaft and extending laterally of the axis, the no-back device comprising a rotary ratchet member and a rotary friction member mounted for limited axial movement within a recess defined by a housing, the no-back device defining at least one path for passing fluid through the recess, the no-back device further comprising peripherally extending diversion means disposed between an outer periphery of the friction member and an inwardly facing peripheral surface of the housing whereby, in use, fluid passing through the recess is diverted away from the inwardly facing peripheral surface of the housing and across a laterally extending surface of the friction member.
In this manner, flow of fluid over critical friction surfaces can be controlled and promoted, thereby facilitating effective cooling and/or lubrication of the device, in use.
The diversion means may be a seal.
Preferably, the no-back device includes a passage for fluid communication between said laterally extending surface of the friction member and a further laterally extending surface of the friction member on an opposite side of the friction member.
The passage may be a through hole in the friction member.
The first-mentioned laterally extending surface of the friction member may include a laterally extending channel for channelling fluid across said first-mentioned surface.
Said further laterally extending surface of the friction member may include a respective further laterally extending channel for channelling fluid across said further surface.
The first-mentioned channel and said further channel may be interconnected for fluid communication by said passage.
Preferably, the no-back device is adapted to receive, in use, the brake element of the screw shaft within said recess such that the brake element is disposed axially adjacent the friction member, thereby promoting dispersal of fluid passing across one of said laterally extending surfaces of the friction member over that surface.